, which, according to documentation should multiplex video and audio stream into a single MKV file without re-conversion. This is indeed the case for the audio stream, however for the video stream it performs completely unnecessary h264 -> libx264 conversion.

The ffmpeg executable in question is statically built with MinGW build environment to include libx264, using the Git repository source code, downloaded on 16.09.2011.

It should be also noted, that such problem doesn't occur, when the executable is build from the 0.8.3 release source code.